An outstanding issue with respect to hair colorants includes ease of application and concerns over messy application resulting in skin staining and uneven hair color results. Recent trends indicate that consumers find handling of foamed products preferable to gels, creams or liquids.
A way to generate a foam product is via a non-pressurized dispenser in the form of a pump foamer or squeeze foamer. The non-pressurized dispensers can be difficult to utilize with hair colorant composition due to the rheology limitations on such systems. As a user supplies the force needed to dispense the product repeatedly, the rheology must be kept to a range that allows for ease of repeated dispensing without fatigue of the user's hands while still providing an acceptable foamed product.
Oxidative hair colorant compositions utilizes dye precursors that are in the form of salts, the first portion of the salt provides the chromophore precursor while the second portion of the salt is a cation or anion. The second portion does not contribute to the chromophore formation.
The formulation window, or available volume, for dye precursors becomes relatively limited when large amounts of dye precursors are needed to achieve the desired end color for the hair, such as brown and black end hair colors. Therefore, it would be a benefit to control the amount of the second portion of the dye precursor through the use of an oxidation-insensitive free base dye precursor. An oxidation-insensitive free base dye precursor would eliminate the second portion of a traditional salt, the second portion not contributing to the chromophore formation. The amount of dye precursor can be increased within the formulation window of the hair colorant composition with the elimination of a cation or anion that does not contribute to the chromophore formation.
It is known that salt content affects the rheology profile by increasing mixed viscosity when salt levels are relatively lower and decreasing mixed viscosity when salt levels are relatively higher. So while more efficient dye precursor loading in the formulation window results from reducing the second portion of the dye precursors allows for, it also results in a hair colorant composition mixed viscosity that is too difficult to dispense through a manually-actuable, non-aerosol dispenser.
Nevertheless such foam oxidative hair colourant compositions must continue to meet consumer expectations with regard to the overall consumer application experience and overall colour result. In particular such products need to be easy and quick to apply and use, deliver only low levels of skin staining and deliver the anticipated overall colour result which is maintained over the subsequent wash cycles. Moreover, the foam must be readily generated and expelled from the dispenser with only minimal foam generation within the dispenser itself and have sufficient durability to be applied onto the hair prior to collapse upon massaging to ensure complete distribution over the entire head of hair.
It has been found that having a particular rheological profile of the oxidative hair coloring composition reduces messy application issues and allows for ease in dispensing while still allowing for an efficient dye precursor loading into the hair colorant composition.